1. Field of the Invention
The invention relates to an exhaust emission control apparatus for internal combustion engines and a process for operating it. The invention also relates to a computer program for executing this process.
2. Prior Art
Exhaust emission control apparatuses particularly for diesel engines are fundamentally known from the prior art. They are situated in the exhaust flow of diesel engines and typically include a diesel oxidizing converter, followed by a particulate filter. There are several known types of particulate matter filters. In diesel vehicles, standard so-called ceramic honeycomb filters with a monolithic structure are usually used. But pocket filters are also known, which have a structure entirely different from that of a honeycomb filter. The filters do not contain capillaries, but instead contain filter pockets, preferably comprised of sintered metal, and the exhaust flows through the surface of these filter pockets. As the exhaust passes through, the particulate matter contained therein is preferably deposited on the surfaces of the pocket filter.
A common trait of all particulate filters is that particulate matter that has been filtered from the exhaust during operation of the diesel engine accumulates inside the filter. Consequently, if the diesel engine were operated for an excessively long time, an excessive particulate mass would accumulate inside the particulate filter, which would in time choke off the exhaust path, thus causing the engine to break down if the accumulated particulate mass were not removed from time to time.
The periodic removal of accumulated particulate mass usually occurs by switching the particulate filter into a so-called regeneration operating mode. The particulate filter is regularly switched into this mode whenever the diesel engine has driven the vehicle a predetermined distance, for example every thousand kilometers, or whenever a certain particulate mass has accumulated inside the particulate filter. The particulate filter is switched into this regeneration operating mode during a normal operation of the diesel engine by raising the operating temperature of the filter to approximately 600° Celsius through suitable engine measures. Suitable engine measures are those that produce an at least temporary increase in the temperature of the exhaust to the above-mentioned temperature value. This can, for example, be achieved by reducing the supply of fresh air or through a combustion of fuel in the preceding catalytic converter. Both measures lead to the desired increase in the temperature of the exhaust flowing through the particulate filter, thus also effecting the desired increase in its operating temperature. In the regeneration mode occurring at this increased operating temperature, the particulate matter accumulated in the particulate filter is burned off. This combustion occurs exothermically and thus leads to a further pronounced temperature increase beyond the 600° C. temperature mentioned as an example above. The regeneration breaks down the accumulated particulate mass inside the particulate filter by essentially converting the particulate matter into carbon dioxide; this improves the flow through the particulate filter once more, almost restoring it to its initial state. Knowledge of the temperature behavior inside the particulate filter during an above-described regeneration process makes it possible to glean information about the particulate mass combusted and therefore broken down during the regeneration described above, as well as information about the speed at which the particulate matter combustion occurs, i.e. the so-called burn rate.
In the standard honeycomb filters that have been used up to this point, a precise detection of the temperature inside these particulate filters has not been possible because installing a temperature sensor laterally inside these particulate filters, perpendicular to the flow direction, would destroy their filter function; more precisely stated, the installation of the temperature sensor would destroy the capillary honeycomb structure and at least part of the exhaust would then escape unfiltered from the honeycomb structure and flow out into the environment. For this reason, up to this point, only the temperature of the exhaust at the exit from the particulate filter has been measured and possibly also the temperature at the entry into the particulate filter so that evaluation of the temperature values thus detected permits inferences to be drawn about the actual temperature behavior inside the particulate filter. The above-described process, however, yields only an imprecise estimate of the temperature sought, thus permitting only the above-indicated imprecise, calculation-based inferences to be drawn regarding the breakdown of the particulate mass during the regeneration.
It is the object of the present invention is to modify a known exhaust emission control apparatus, to provide a process for its operation, and to provide a corresponding computer program so as to enable a more precise detection of the temperature of the exhaust inside a particulate filter, in particular during the regeneration operation.